Sidewall unit, fabricating method thereof, and fluid storage tank comprising the sidewall unit

ABSTRACT

A method of fabricating a sidewall unit includes a step of providing members configuring the sidewall units, a step of forming a first joint structure, a first step of eliminating distortion, a step of forming a second joint structure, and a step of assembling a sidewall unit. The step of eliminating distortion is a step to eliminate distortion due to heat generated when welding members. In the step, a force substantially vertical to a flange surface and a force substantially horizontal to the flange surface are applied to a joint structure before joining the joint structure and a sidewall panel. A fluid storage tank using the sidewall units according to the present invention can securely prevent leakage of fluid even when a large quantity of fluid is stored therein.

TECHNICAL FIELD

The present invention relates to a knockdown-type fluid storage tank, and in particular, the present invention relates to a sidewall unit and a manufacturing method thereof for a knockdown-type fluid storage tank configured with a plurality of sidewall units, the sidewall unit being fabricated so as to prevent leakage of the fluid from joints between the sidewall units even when a large quantity of fluid is stored inside.

BACKGROUND ART

In general, a fluid storage tank having space inside for storing fluid employs knockdown structure, except when seamless structure may be employed. A knockdown-type fluid storage tank is pre-fabricated in a factory as a plurality of units with predefined size suitable for transportation. The plurality of fabricated units is transported on vehicles to an installation site and is assembled. At the installation site, the plurality of units is joined in circumferential direction to make a cylindrical member, and a plurality of cylindrical member is stacked in height direction to assemble a fluid storage tank. Herein, “circumferential direction” and/or “circumferential” refer to a direction parallel to ground and “height direction” refers to a direction perpendicular to the circumferential direction. Various tanks, such as a cylindrical storage tank disclosed in Patent Document 1, are proposed as a knockdown-type fluid storage tank.

For a knockdown-type fluid storage tank, it is important how to prevent leakage of fluid from joints between the units. The following techniques are, for example, proposed to prevent leakage of fluid in existing knockdown-type fluid storage tanks.

The technique disclosed in Patent Document 2 is to prevent leakage with an improved joint structure between units. The technique disclosed in claims, FIG. 5 and FIG. 6 of Patent Document 2 proposes an edge structure of each of the units such that a trough is formed at a joint between two units and a paste sealant is filled into the trough. As the technique of Patent Document 2, various other techniques for preventing leakage of fluid with a joint structure are proposed.

The technique disclosed in Patent Document 3 is to prevent leakage with an improved application method of a sealant at a joint. In the technique disclosed in Patent Document 3, a moisture-curing sealant is applied from a side corresponding to an internal side of a tank. When a surface of the sealant is subsequently cured, water is filled in the tank. By filling water in the tank, a pressure of water forces joints to open a little to allow for uncured sealant entering inside the joints to improve water sealing at the joints.

The technique disclosed in Patent Document 4 is to prevent leakage with combining an improved joint-filling adhesive agent and an improved joint structure. In the technique disclosed in Patent Document 4, an adhesive agent for joint-filling in a tank having one-component moisture-curing resin as a main component and containing a silane coupling agent as an adhesion provider and fiber filler is used to prevent leakage from joints between units. Flanges filled with the joint-filling adhesive agent are covered with metallic pressing members so that entire flange is covered.

Patent Document 5 proposes a fluid storage tank configured by mutually joining end edges of a plurality of plate body which allows for improving workability during assembly and for reducing related costs without deteriorating storage performance. For a knockdown-type fluid storage tank, it is necessary to consider workability during assembly of the fluid storage tank.

The prior art documents referred to in the above descriptions are listed below.

-   Patent Document 1: Japanese Laid-Open Patent Publication     2009-012849A -   Patent Document 2: Japanese Patent No. 63-006432B -   Patent Document 3: Japanese Laid-Open Patent Publication     2010-013155A -   Patent Document 4: Japanese Laid-Open Patent Publication     2005-105083A -   Patent Document 5: Japanese Laid-Open Patent Publication 08-026381A

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

It is naturally a major premise that leakage of fluid from joints is securely prevented in a knockdown-type fluid storage tank, but at the same time, a structure of joints between units configuring the fluid storage tank and a method for joining the units on site are required to be simple as much as possible from a viewpoint of ease of on-site assembly and de-assembly and of fabricating cost. Thus, it is preferable that a bulk fluid storage tank is configured to simplify an assembly process thereof at an installation site such that the tank may be assembled by simply opposing joint flanges of units and joining the joint flanges with mechanical fasteners such as bolts and nuts for mutually joining the units. Such simple-structured unit is also advantageous from a viewpoint of fabricating cost.

Such joint structure and method for joining are also advantageous to be employed for facilitating de-assembly of a fluid storage tank. A bulk fluid storage tank is often not owned by a company which needs the tank, but is leased from a leasing company owning the tank. Then, it is advantageous from a viewpoint of construction schedule and of cost if it is easy to de-assemble the bulk fluid storage tank when returning to the leasing company after use.

However, for example in a bulk fluid storage tank with a capacity of 1,000 m³ or more, there has been a problem as that, since internal pressure acting on units located in lower part of the tank was extremely large, a slight distortion on a joint flange surface of the units could have caused leakage of the fluid from the joints between the units.

Even though various conventional techniques such as those described in the above have been proposed to prevent leakage of fluid, since the conventional techniques did not consider removal of distortion due to welding heat at the joints when assembling a tank, it was extremely difficult to solve the problem of leakage especially in a bulk fluid storage tank storing fluid of a certain level or more and the problem of ease of assembly and de-assembly of the tank at the installation site and of fabricating cost, and thus, it has been difficult to employ the conventional techniques in the bulk fluid storage tank.

The present invention aims at providing a sidewall unit configuring at least a part of a fluid storage tank which does not cause leakage of fluid from joints between the units even when a large quantity of fluid above a certain level is stored, and a fluid storage tank using such sidewall units.

Means for Solving the Problem

The above problem may be solved by providing a step of accurately eliminating distortion due to welding heat at joints for joining with other sidewall units during a step of fabricating each of sidewall units configuring at least a part of a fluid storage tank, and by making a structure of the joints including joint flanges as one which does not cause distortion at the joints under a long term use while ensuring workability during joining.

According to a first aspect, the present invention provides a method for fabricating a sidewall unit for use in fabricating a fluid storage tank having at least a bottom wall and a sidewall. The sidewall is configured with one cylindrical member or by stacking a plurality of cylindrical members in height direction, and at least one of the cylindrical members is configured by joining a plurality of sidewall units in circumferential direction. The method comprises a step of providing members configuring the sidewall unit, a step of forming a first joint structure, a first step of eliminating distortion, a step of forming a second joint structure, and a step of assembling a sidewall unit. In the step of providing members configuring the sidewall unit, a rectangular sidewall plate and members included in a joint structure to be mounted to each of two opposing circumferential edges of the sidewall plate are prepared, wherein the members include a base member having long sides and short sides, a circumferential joint flange having long sides and short sides, and a plurality of reinforcing members having two adjacent edges which intersect at a predetermined angle.

In the step of forming a first joint structure, the first joint structure is formed by coupling the circumferential joint flange with the base member in a positional relationship where a long side of the circumferential joint flange and a long side of the base member are parallel such that a non-flange surface on the other side of a flange surface of the circumferential joint flange intersects with one of surfaces of the base member at a predetermined angle, and by coupling at least a part of each of the two adjacent edges respectively with the non-flange surface of the circumferential joint flange and the one of surfaces of the base member such that the plurality of reinforcing members stand with an interval with each other on a side of an inner angle formed by the non-flange surface of the circumferential joint flange and the one of surfaces of the base member. Distortion in the first joint structure is eliminated in a first step of eliminating distortion by simultaneously applying a force from the non-flange surface to the flange surface and a force from the flange surface to the non-flange surface respectively to a center part and to both ends in the longitudinal direction of the first joint structure.

The present method further comprises a step of forming a second joint structure where the second joint structure is formed in similar steps as providing members, forming the first joint structure and eliminating distortion, and a step of assembling the sidewall unit where one of the opposing circumferential edges of the curved sidewall plate is coupled with the long side of the base member of the first joint structure and the other of the opposing circumferential edges of the curved sidewall plates is coupled with the long side of the base member of the second joint structure.

According to a second aspect, the present invention also provides a method for fabricating a sidewall unit used in fabricating a fluid storage tank having at least a bottom wall and a sidewall as in the first aspect. The sidewall is configured with one cylindrical member or by stacking a plurality of cylindrical members in height direction, and at least one of the cylindrical members is configured by joining a plurality of sidewall units in circumferential direction. The present method comprises a first step of eliminating distortion and forming a first joint structure to form the first joint structure while eliminating distortion, in place of the step of forming the first joint structure and the first step of eliminating distortion which are performed as separate steps in the first aspect.

In the first step of eliminating distortion and forming a first joint structure, a first intermediate structure is formed by temporarily coupling the circumferential joint flange with the base member in a positional relationship where a long side of the circumferential joint flange and a long side of the base member are parallel such that a non-flange surface on the other side of a flange surface of the circumferential joint flange intersects with one of surfaces of the base member at a predetermined angle, and by temporarily coupling at least a part of each of the two adjacent edges respectively with the non-flange surface of the circumferential joint flange and the one of surfaces of the base member such that the plurality of reinforcing members stand with an interval with each other on a side of an inner angle formed by the non-flange surface of the circumferential joint flange and the one of surfaces of the base member. Then, a second intermediate structure is formed by the same step as the step of forming the first intermediate structure. Then, while temporary binding the first intermediate structure and the second intermediate structure, a circumferential joint flange, each of the plurality of reinforcing members and the base member of at least the first intermediate structure are coupled with each other and the temporary biding of the first intermediate structure and the second intermediate structure is released to obtain the first joint structure. The second joint structure may be formed from the second intermediate structure.

In one embodiment of the second aspect, the method may further comprise a second step of eliminating distortion to eliminate distortion from the first joint structure, after the first step of eliminating distortion and forming a first joint structure, by simultaneously applying a force from the non-flange surface to the flange surface and a force from the flange surface to the non-flange surface respectively to a center part and to both ends in the longitudinal direction of the first joint structure.

In one embodiment of the first and the second aspect, the method may further comprise a third step of eliminating distortion to eliminate distortion from the first joint structure by simultaneously applying a force from one of surfaces of the base member to a surface opposite to the one of the surfaces of the base member and a force from the surface opposite to the one of the surfaces of the base member to the one of the surfaces of the base member respectively to a center part and to both ends in the longitudinal direction of the first joint structure.

In one embodiment, coupling and/or temporary coupling of members may be performed by following a sequence of a step of coupling a circumferential joint flange with each of a plurality of reinforcing members, a step of coupling the circumferential joint flange with a base member, and a step of coupling the plurality of reinforcing members with the base member. In another embodiment, coupling and/or temporary coupling of members may also be performed by following a sequence of a step of coupling a circumferential joint flange with a base member, and a step of coupling each of a plurality of reinforcing members respectively with the circumferential joint flange and the base member. In addition, it is preferable that coupling and/or temporary coupling of the circumferential joint flange, the base member and the plurality of reinforcing members is sequentially performed from coupling positions in vicinity of the center part to coupling positions toward short side with respect to a long side of the circumferential joint flange.

Since the present invention allows for effective elimination of distortion in the circumferential joint flange due to welding heat when mutually coupling members configuring the sidewall unit in fabricating the sidewall unit configuring at least a part of a fluid storage tank, the sidewall units may be accurately mutually joined. Generation of distortion in the circumferential joint flange due to welding heat to weld the base member and the sidewall plate may be reduced by having a base member, a rigid body with a short side of predetermined length, intervene between the circumferential joint flange and the sidewall plate, instead of directly coupling the circumferential joint flange and the sidewall plate. Further, when a high pressure is generated by fluid in a tank, there may be a case where a conventional technique of directly coupling the circumferential joint flange and the sidewall plate is not enough to maintain an angle formed by the circumferential joint flange and the sidewall plate, and a flange surface of an adjacent circumferential joint flange may be pressed to open from inside. The present invention, on the other hand, can maintain an angle formed by a base member and the circumferential joint flange by having the base member, a rigid body with a greater thickness than that of the sidewall plate, intervene therebetween, and thus, a flange surface of an adjacent circumferential joint flange may not be pressed to open from inside, thereby a joint between the circumferential joint flanges may be improved.

In another embodiment of the present invention, it is preferable that a plurality of reinforcing members are coupled such that a space between the plurality of reinforcing members is smaller in a center part than that in end parts in the long side of the circumferential joint flange. A reinforcing member may be a panel and may comprise: a first edge which is longer than a short side of a base member and is coupled with the base member and a sidewall plate; a second edge which intersects with the first edge at a predetermined angle and is coupled to a non-flange surface; a third edge which opposes to the first edge and has a length corresponding to a short side of the base member; and a fourth edge which opposes to the second edge and connects one end of the first edge with one end of the third edge. In a plurality of reinforcing member, it is preferable that a notch part is formed in one or both of a portion corresponding to a crossing point of the first edge and the second edge and a portion corresponding to a coupling point of the base member and the sidewall plate at the first edge.

Adopting such mounting position and shape of reinforcing member allows for welding a circumferential joint flange and a base member while maintaining an angle formed therebetween. Since a plurality of reinforcing member allows for maintaining the angle formed between the circumferential joint flange and the base member even when a high pressure is generated by fluid in a tank, a flange surface of adjacent circumferential joint flanges is not pressed to open from inside and leakage of the fluid may be prevented.

In another embodiment of the present invention, it is preferable that the method further comprises a step of forming a plurality of holes for passing mechanical fasteners over a long side of the circumferential joint flange, and that the plurality of holes are formed such that a diameter thereof is larger in a center part than that at an end of the long side of the circumferential joint flange. It is also preferable that the method further comprises a step of forming a groove in a flange surface of the circumferential joint flange for inserting a sealing layer.

Joint strength between the circumferential joint flanges may be further increased by varying strength of the mechanical fasteners used for joining the circumferential joint flanges. In addition, leakage of fluid in a tank may be securely prevented and displacement of the sealing layer during assembling the fluid storage tank may be avoided by providing a groove in a flange surface of the circumferential joint flange for forming a sealing layer.

According to a third embodiment, the present invention provides a sidewall unit configuring a cylindrical member, the sidewall unit used in a fluid storage tank having at least a bottom wall and a sidewall configured with one cylindrical member or by stacking a plurality of cylindrical members in height direction, the fluid storage tank being configured by joining a plurality of sidewall units in circumferential direction. The sidewall unit comprises a curved rectangular sidewall plate and a pair of joint structures mounted to each of two opposing circumferential edges of the sidewall plate, and each of the pair of joint structures includes a base member having long sides and short sides, a circumferential joint flange having long sides and short sides, and a plurality of reinforcing members having two adjacent edges which intersect at a predetermined angle.

The circumferential joint flange and the base member are coupled in a positional relationship where a long side of the circumferential joint flange and a long side of the base member are parallel such that a non-flange surface on the other side of a flange surface of the circumferential joint flange intersects with one of surfaces of the base member at a predetermined angle. Each of two adjacent edges of each of a plurality of reinforcing members is coupled respectively with the non-flange surface of the circumferential joint flange and the one of surfaces of the base member such that the plurality of reinforcing members stands with an interval with each other on a side of an inner angle formed by the non-flange surface of the circumferential joint flange and the one of surfaces of the base member. Long side of the base member in each of the pair of joint structures is coupled to each of the opposing circumferential edges of the sidewall plates.

Use of the sidewall unit with such structure allows for maintaining the angle formed between the circumferential joint flange and the base member, and since the angle formed between the circumferential joint flange and the base member may be maintained even when a high pressure is generated by fluid in a tank, a flange surface of adjacent circumferential joint flanges is not pressed to open from inside and leakage of the fluid may be prevented.

According to a fourth aspect, the present invention provides a fluid storage tank comprising sidewall units fabricated with a method according to any one of claim 1 to claim 16.

According to a fifth aspect, the present invention provides a fluid storage tank comprising sidewall units according to any one of claim 17 to claim 25.

According to the present invention, a fluid storage tank, in which leakage of fluid is securely prevented even when a large quantity of fluid is stored, may be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a bulk fluid storage tank assembled using sidewalls according to one embodiment of the present invention.

FIG. 2 is a perspective view of a bulk fluid storage tank assembled using sidewalls according to another embodiment of the present invention.

FIG. 3 is a perspective view of a sidewall according to one embodiment of the present invention.

FIG. 4A is a perspective view of a part of a joint structure and a sidewall plate included in a sidewall unit shown in FIG. 3.

FIG. 4B is a perspective view showing another embodiment of a joint structure.

FIG. 4C is a perspective view showing further embodiment of a joint structure.

FIG. 5( a) is a perspective view showing a shape of a reinforcing member shown in FIG. 4.

FIG. 5( b) is a perspective view showing another shape of a reinforcing member.

FIG. 6 is a view for describing a method to eliminate distortion in a joint structure.

FIG. 7 is a view for describing a method to eliminate distortion in a joint structure in a direction different from FIG. 6.

FIG. 8 is a view for describing a method to form a joint structure while eliminating distortion therein.

FIG. 9 is a view for describing a method to form a joint structure while eliminating distortion therein.

FIG. 10 is a perspective view showing a groove for arranging a sealing layer provided on a joint flange surface.

FIG. 11 is a perspective view of a sidewall unit provided with a joint flange in height direction.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be described with reference to specific embodiments illustrated in the accompanying drawings.

1. Structure of Sidewall Unit

FIG. 1 shows an example of a bulk fluid storage tank assembled using sidewalls according to one embodiment of the present invention. A sidewall unit comprises joint structures on both circumferential ends, and each of the joint structures comprises a circumferential joint flange. The fluid storage tank is assembled by joining a plurality of sidewall units in circumferential direction by mutually joining joint structures via a circumferential joint flange and stacking a plurality of cylindrical members formed with a plurality of joined sidewall units in height direction on a bottom wall separately fabricated. Herein, “cylindrical member” is not limited to what is circular cylindrical body but may include what is a polygonal cylindrical body. A number of sidewall units and cylindrical members to be used is not limited but may be appropriately selected depending on a size and an application of a fluid storage tank. A sidewall unit according to the present invention is more preferably used for a bulk fluid storage tank with a capacity of at least 1,000 m³ or more, and can securely prevent leakage of fluid from joints between the sidewall units even when used for a fluid storage tank with an inner diameter of 12 m or more, a height of 10 m or more and a capacity of 1,200 m³ or more.

A sidewall unit according to the present invention is fabricated with a fabricating step including a step of eliminating distortion in a joint structure generated due to welding heat, and owing to the step of eliminating distortion, the sidewall unit which does not cause leakage of fluid from joints between adjacent sidewall units even when a high inner pressure acts on the fluid storage tank may be obtained. A joint structure of the sidewall unit according to the present invention has a special structure which will be described in detail in the following, and owing to the special structure, deformation of the joint structure may be prevented because an angle formed by a circumferential joint flange and a base member is maintained even when a high inner pressure is applied thereto. Further, the special structure prevents deformation of coupling between the joint structure and the sidewall plate, and thus, effect of prevention of leakage of fluid is extremely great even if a high inner pressure acts over a long term, no need to mention over a short term. In a bulk fluid storage tank, inner pressure acting on a sidewall especially at a lower part of the tank is very large, but elimination of distortion due to heat under fabrication of joints between sidewall units was not conventionally considered, and thus, it was not possible to securely prevent leakage of fluid from the joints in conventional sidewall units which did not comprise the special structure as the joint structure of the present invention.

The following are two main forms of a fluid storage tank using sidewall units, and the sidewall unit according to the present invention may be used in a fluid storage tank in any forms including the following forms. One of the two forms is a fluid storage tank 1 of cylindrical member stack type as shown in FIG. 1. In the fluid storage tank 1 of cylindrical member stack-type, a plurality of side wall units 10 mounted with a joint structure to each of circumferential edges (i.e. short sides) of a horizontally oriented sidewall plate are joined in circumferential direction to form a cylindrical member 2, and a plurality of cylindrical members 2 are stacked in height direction on a bottom wall to be used as a sidewall. Since inner pressure acting on upper portion of the fluid storage tank 1 is smaller than that on lower portion, the sidewall unit 10 according to the present invention may not necessarily be used in the cylindrical members 2 configuring the sidewall in the upper portion. That is, the sidewall unit according to the present invention may be used for units positioned in lower portion of the fluid storage tank 1, and conventional units may be used for units positioned in upper portion of the fluid storage tank 1.

The other of the two forms is a fluid storage tank 1′ of a single cylindrical member type as shown in FIG. 2. In the fluid storage tank 1′ of a single cylindrical member type, a plurality of side wall units 10′ mounted with a joint structure to each of circumferential edges (i.e. long sides) of a vertically oriented sidewall plate are joined in circumferential direction to form a cylindrical member 2′ on a bottom wall, and a single cylindrical member 2′ is used as a sidewall of the fluid storage tank 1′. In this case, all sidewall units should be the sidewall unit according to the present invention.

Now, a structure of a sidewall unit 10 according to one embodiment of the present invention is described with a fluid storage tank 1 of stack type shown in FIG. 1 as an example. FIG. 3 shows a sidewall unit 10 according to one embodiment of the present invention. The sidewall unit 10 comprises one sidewall plate 12 and two joint structures 22, 24 mounted to each of opposing circumferential edges 14, 16 of the sidewall plate 12. In the following, the present invention will be described based on an example where one cylindrical member 2 is configured with four horizontally oriented sidewall units as shown in FIG. 1.

(Joint Structure)

FIG. 4A shows a joint structure 22 mounted to the circumferential edge 14 of the sidewall plate 12. Since a joint structure 24 normally has a same structure as the joint structure 22, only the joint structure 22 will be described in detail in the following. The joint structure 22 has a base member 26, a circumferential joint flange 28 and a plurality of reinforcing member 30. In FIG. 4A, the sidewall plate 12 mounted to the joint structure 22 is also shown.

The base member 26 and the circumferential joint flange 28 are coupled such that a non-flange surface 28A which is an opposite surface of a flange surface 28B of the circumferential joint flange 28 intersects with one of surfaces 26A of the base member 26 at a predetermined angle. The predetermined angle is an angle determined depending on a diameter of the fluid storage tank 1, and is preferably be 90 degrees or larger. This means that it is necessary to arrange the flange surface 28B of the circumferential joint flange 28 vertical with respect to the sidewall of the fluid storage tank 1, while a main surface (i.e. the one of surfaces 26A) of the base member is arranged along the sidewall of the cylindrical fluid storage tank 1. Thus, an intersecting angle between the non-flange surface 28A of the circumferential joint flange 28 and the one of surfaces 26A of the base member 26 is 90 degrees or larger. The intersecting angle may be smaller as the diameter of the fluid storage tank 1 to be assembled is larger, and may be larger as the diameter of the fluid storage tank 1 to be assembled is smaller. A positional relationship between a long side 28L of the circumferential joint flange 28 and a long side 26L of the base member 26 may be substantially parallel. In FIG. 4A, the base member 26 is shown as standing from an end in short side direction of the non-flange surface 28A of the circumferential joint flange 28, but it may be arranged such that the base member 26 stands from a position other than ends of the non-flange surface 28A of the circumferential joint flange 28, such as from center part in the short side direction. In this case, the circumferential joint flange 28 of the sidewall unit 10 intrudes inside the fluid storage tank 1 as shown in FIG. 4B, and, by joining the adjacent circumferential joint flanges 28 with mechanical fasteners for example at the inside portions, the joint strength between the adjacent circumferential joint flanges 28 may be increased to achieve better prevention of leakage of fluid.

In FIG. 4A, the base member 26 is shown as standing from the non-flange surface 28A, but it may be arranges such that the circumferential joint flanges 28 stands from an end in the short side direction of the one of surfaces 26A of the base member 26. However, in such configuration, since a process to shave welding is necessary at a joint between the circumferential joint flanges 28 and the base member 26 in a joint surface for joining the joint structure 22 with other joint structures, not only a number of processes is increased, but also there is a risk that the process results in generating a gap between the flange surface 28B of the circumferential joint flanges 28 and an end surface of the long side 26L of the base member 26. In this case, it is necessary to ensure sufficient accuracy of flatness to avoid leakage of fluid from a joint surface between the joint structure 22 and an adjacent structure.

At least a part of each of the two adjacent edges 30A and 30B of a plurality of reinforcing member 30 is coupled respectively with the non-flange surface 28A of the circumferential joint flange and the one of surfaces 26A of the base member 26 such that the plurality of reinforcing members stands at a predetermined spacing on a side of an inner angle formed by the non-flange surface 28A of the circumferential joint flange 28 and the one of surfaces 26A of the base member 26.

(Sidewall Plate)

The sidewall plate 12 may be a rectangular metal panel with two opposing circumferential edges 14, 16 as short sides and two opposing edges in height direction 18, 20 as long sides. The sidewall plate 12 may be fabricated with any material such as steel or stainless steel depending on fluid to be stored in the fluid storage tank 1 or on life expectancy of the fluid storage tank 1 itself. A shape of the sidewall plate 112 may be any of horizontally oriented rectangular, vertically oriented rectangular or square depending on a shape of the fluid storage tank 1 and a number of sidewall units 10 configuring one cylindrical member 2. Thickness of the sidewall plate 12, length of the circumferential edges 14, 16 and length of the edges in height direction 18, are not limited but may be appropriately selected depending on a size of the fluid storage tank 1. The sidewall plate 12 may be curved to suit curvature of the sidewall of the fluid storage tank 1 at any point of time before the joint structure is mounted to the circumferential edges 14, 16.

(Base Member)

A base member 26 in the embodiment may be a metal panel having two long sides 26L and two short sides 26S. The base member 26 may be fabricated with any material such as steel or stainless steel depending on fluid to be stored in the fluid storage tank 1 or on life expectancy of the fluid storage tank 1 itself. One of the two long sides 26L is an edge to be welded to couple with the circumferential edge 14 of the sidewall plate 12, and thus, a length thereof is preferably equal to a length of the circumferential edge 14. A length of the two short sides 26S may preferably be one which allows for securing a distance where welding heat for welding the base member 26 and the sidewall plate 12 does not give any impact to a later-described circumferential joint flange 28.

Thickness of the base member 26 is not limited but may be appropriately selected depending on a size of the fluid storage tank 1. The base member 26 is preferably fabricated thicker than the sidewall plate 12. Use of the base member 26 thicker than the sidewall plate 12 allows for rigidly maintaining the predetermined angle between the base member 26 and the circumferential joint flange 28. If the sidewall plate is directly coupled with the circumferential joint flange as in the prior art, the angle between the sidewall plate and the flange surface cannot be maintained under a high pressure from fluid inside the tank, the opposing flange surfaces between adjacent sidewall units may be forced to open from a direction corresponding to inside of the tank to cause leakage of the fluid.

(Circumferential Joint Flange)

A circumferential joint flange 28 in the embodiment may be a metal plate having two long sides 28L and two short sides 28S. The circumferential joint flange 28 may be fabricated with any material such as steel or stainless steel depending on fluid to be stored in the fluid storage tank 1 or on life expectancy of the fluid storage tank 1 itself. Length of the long side 28L is preferably equal to that of the long side 26L of the base member 26. Thickness and length of the short side 28S of the circumferential joint flange 28 are not limited but preferably are ones sufficient for securing joint strength with the circumferential joint flanges 28 of adjacent sidewall units 10.

In the circumferential joint flange 28, holes 32 for passing through fasteners such as bolts and nuts to mechanically join the circumferential joint flange 28 with other circumferential joint flanges 28 of adjacent sidewall units 10 may be provided. The hole 32 may not necessarily be provided at an even interval with respect to the long side direction of the circumferential joint flange 28, but may be provided at any interval depending on necessity. For example, inner pressure which deforms a sidewall to outwardly bulge acts to the sidewall 10 in a bulk fluid storage tank at a center part in height direction which is away from a joint in height direction. To address this, intervals between adjacent holes 32 may be smaller (i.e. a number of the holes 32 is increased) toward the center part from an edge in the long side direction (i.e. in the height direction) of the circumferential joint flange 28 in order to improve joint strength at corresponding portions of the circumferential joint flange 28, as shown in FIG. 4C. Beside varying intervals between the holes 32, or along with varying the intervals thereof, a diameter of the hole 32 may be increased for passing through a bolt with a larger diameter in order to improve joint strength of the circumferential joint flanges 28. Positions of the holes 32 are preferably closer to the base member as much as possible.

(Reinforcing Member)

Each of a plurality of reinforcing member 30 may be a metal plate and may be what has at least a first edge 30A at least a part of which is welded to the one of surfaces 26A of the base member 26 and a second edge 30B which intersects with the first edge 30A at a predetermined angle and is welded to at least a part of the non-flange surface 28A of the circumferential joint flange 28. Thus, the predetermined angle between the base member 26 and the circumferential joint flange 28 may be maintained owing to the first edge 30A and the second edge 30B. The predetermined angle is an angle which may be determined depending on a diameter of the fluid storage tank 1 as above described. Lengths of the first edge 30A and the second edge 30B are not limited. However, it is preferable that the length of the first edge 30A is equal to that at least of the short side 26S of the base member 26. In another embodiment, it is preferable that the first edge 30A is longer than the short side 26S of the base member 26 and is also welded to a surface 12A of the sidewall plate 12. Deformation of coupling between the base member 26 and the sidewall plate 12 against inner pressure may be avoided and strength of the sidewall plate 12 against inner pressure may be increased by making the length of the first edge 30A sufficient to cross from the one of surfaces 26A of the base member 26 to the surface 12A of the sidewall plate.

The reinforcing member 30 may further be what has a third edge 30C having a length corresponding to the short side 26S of the base member 26 and a fourth edge 30D opposing to the second edge 30B and connecting one end of the first edge 30A with one end of the third edge 30C, as shown in FIG. 5( a). A length of the third edge 30C is preferably equal to that of the short side 26S of the base member 26. In this case, the reinforcing member 30 is shaped as a combination of a rectangle formed with the first edge 30A, the second edge 30B and the third edge 30C and a triangle where a portion of the first edge 30 a to be coupled to the surface 12A of the sidewall plate 12 and the fourth edge 30D are two adjacent sides. By shaping the reinforcing member 30 as such, the rectangle portion serves to retain the angle between the base member 26 and the circumferential joint flange 28 and the triangle portion serves to reinforce strength of the sidewall plate 12 against inner pressure, and as a result, leakage of fluid from joints between adjacent sidewall units 20 may be securely prevented even in a bulk fluid storage tank where an inner pressure may be large.

In a plurality of reinforcing member 30, it is preferable that a notch 31 is formed at a portion corresponding to a crossing point of the first edge 30A and the second edge 30B, as shown in FIG. 5( b). In a reinforcing member 30 without a notch 31, there is a risk of stress concentrating to a crossing point of a first edge 30A and a second edge 30B when inner pressure acts on a joint structure 22 and failure of the reinforcing member 30 is initiated from the crossing point. Generation of such failure may be prevented by providing the notch 31. Without the notch 31, welding of the base member 26 with the circumferential joint flange 28 may be discontinuous at the crossing point of the first edge 30A and the second edge 30B. Providing the notch 31 is also advantageous in that the base member 26 and the circumferential joint flange 28 may be continuously welded.

In the embodiment, it is preferable that a step is provided in halfway of the first edge 30A as shown in FIG. 5( a). This is because that the reinforcing member 30 is formed to correspond to a step between the one of surfaces 26A of the base member 26 and an outer surface 12A of the sidewall plate 12 generated by coupling the other surface 26B of the base member 26 with an inner surface 12B of the sidewall plate 12 to accommodate that the base member 26 being thicker than the sidewall plate 12, as shown in FIG. 4A. Thus, when the reinforcing member 30 is used in an embodiment where the one of surfaces 26A of the base member 26 is coupled to be approximately flush with the outer surface 12A of the sidewall plate, there is not need to provide any step in the first edge 30A. In another embodiment, it is more preferable that a notch 34 is formed at a portion corresponding to a coupling point of the sidewall plate and the base member 26, i.e. at a portion corresponding to the step in the first edge 30A, as shown in FIG. 5( b). Forming the notch 34 may provide effect of preventing concentration of stress at a step and discontinuous welding between the sidewall plate 12 and the base member 26, as the effect of the notch 31.

Although an interval between each of a plurality of reinforcing member 30 is even in the embodiment, it is not limited as such and the plurality of reinforcing members 30 may be provided at any interval depending on necessity. In another embodiment, a plurality of reinforcing member 30 may be coupled at a smaller interval in vicinity of a center part in a long side direction of the circumferential joint flange 28 than at an end thereof, as shown in FIG. 4C. It may be possible to effectively resist against inner pressure acting at the center part in height direction of the sidewall unit 10 by coupling the reinforcing members 30 at such interval.

2. Fabricating Method of Sidewall Unit

Next, a fabricating method of sidewall unit according to the present invention will be described using the sidewall unit 10 shown in FIG. 3 as an example with reference to FIG. 6 to FIG. 9.

(Preparation of Members)

In the method, members configuring the sidewall unit 10 are firstly prepared. As above described, one sidewall unit 10 comprises at least one sidewall plate 12 and two joint structures 22, 24, and each of the joint structures 22 and 24 comprises at least one base member 26, one circumferential joint flange 28, and a plurality of reinforcing member 30. A number of the reinforcing member 30 is not limited but may be appropriately selected according to inner pressure acting on inner wall of the fluid storage tank 1. A number of sidewall unit 10 used in the fluid storage tank 1 may be appropriately selected according to size, application and inner pressure of the fluid storage tank 1, thus, numbers of members prepared for fabricating one fluid storage tank 1, i.e. sidewall plate 12, base member 26, circumferential joint flange 28 and reinforcing member 30, may be varied depending on a number of the sidewall units 10 to be used. For example, when the fluid storage tank 1 is configured with four cylindrical members 2 and one cylindrical member 2 is configured with four sidewall units 10, then a number of sidewall units 10 to be used is 16.

(1) First Embodiment Fabricating without Temporary Assembling

Fabricating method according to the first embodiment of the present invention may comprise a step of forming a first joint structure, a first step of eliminating distortion, a step of forming a second joint structure, and a step of assembling a sidewall unit. Depending on necessity, the method may comprise a third step of eliminating distortion and/or an auxiliary step of eliminating distortion. Unlike a fabricating method according to the second embodiment described later, the fabricating method according to the first embodiment is a method to form a joint structure without temporary assembly of joint structures.

(Step of Forming a First Joint Structure)

A step of forming a first joint structure is a step for forming a joint structure 22 or 24. Here, the joint structure 22 is described as the first joint structure shown in FIG. 4A. In this step, each of members is firstly arranged in a predetermined position such that a non-flange surface 28A which is an opposite surface of a flange surface 28B of a circumferential joint flange 28 matches with one of end surfaces of two long sides 26L of a base member 26. At this point, one of surfaces 26A of the base member 26 and the non-flange surface 28A are positioned to intersect at a predetermined angle. In addition, a plurality of reinforcing member is arranged with an interval with each other on a side of an inner angle formed by the non-flange surface 28A of the circumferential joint flange 28 and the one of surfaces 26A of the base member 26. A plurality of reinforcing member 30 is preferably arranged such that a main surface of the reinforcing member 30 is perpendicular to any of the one of surfaces 26A and the non-flange surface 28A. A positional relationship of a long side 28L of the circumferential joint flange 28 and a long side 26L of the base member 26 may be substantially parallel.

Next, the long side 26L of the base member 26 and the non-flange surface 28A of the circumferential joint flange 28, the one of surfaces 26A of the base member 26 and at least a part of a first edge 30A of the reinforcing member 30, and the non-flange surface 28A of the circumferential joint flange 28 and at least a part of a second edge 30B of the reinforcing member 30 are all coupled by welding. Coupling here means welding the circumferential joint flange 28 and a plurality of reinforcing member 30 with strength sufficient to secure durability against inner pressure when assembled as a fluid storage tank. Herein, it may be called as a final coupling.

In general, heat shrink of material occurs when a welded part cools down. Thus, when a side of the long side 26L facing to the one of surfaces 26A of the base member 26 and the non-flange surface 28A of the circumferential joint flange 28 are welded, a force acts to the base member 26 and the circumferential joint flange 28 as to reduce the inner angle formed by the one of surfaces 26A and the non-flange surface 28A smaller than the predetermined angle. However, in the present invention, an angle formed by the one of surfaces 26A and the non-flange surface 28A may be maintained against heat shrink caused by cooling of welding heat by arranging the reinforcing members 30 which an angle formed by the first edge 30A and the second edge 30B is the predetermined angle in advance between the one of surfaces 26A and the non-flange surface 28A.

Sequence of coupling the base member 26, the circumferential joint flange 28 and a plurality of reinforcing member 30 is not particularly limited. In one embodiment, coupling the base member 26, the circumferential joint flange 28 and a plurality of reinforcing member 30 may be done in a sequence of firstly coupling the circumferential joint flange 28 and each of a plurality of reinforcing member 30, then coupling the circumferential joint flange 28 and the base member 26, and finally coupling a plurality of reinforcing member 30 and the base member 26. In another embodiment, coupling the base member 26, the circumferential joint flange 28 and a plurality of reinforcing member 30 may be done in a sequence of firstly coupling the base member 26 and the circumferential joint flange 28, then coupling each of a plurality of reinforcing member 30 and the base member 26 and the circumferential joint flange 28. In view of minimizing generation of distortion due to welding heat, it is more preferable to couple the circumferential joint flange 28 and a plurality of reinforcing member 30 sequentially from a coupling point in vicinity of a center part in a long side direction of the circumferential joint flange 28 to a coupling point at an end thereof.

(First Step of Eliminating Distortion)

For a fabricating method of a sidewall unit according to the present invention, it is most important to eliminate any distortion in a joint structure so that the joint structure can withstand high inner pressure acting in a fluid storage tank fabricated by joining sidewall units. To achieve this, the present invention is characterized in that it comprises a step of eliminating distortion due to welding in a joint structure during a step of fabricating a sidewall unit. FIG. 6 shows a first step of eliminating distortion in a fabricated joint structure 22.

Degree of shrinking due to welding heat increases with increase of welding length in welded members. Thus, the joint structure 22 is distorted as that a center part of the circumferential joint flange 28 in a long side (28L) direction protrudes to a side of the non-flange surface 28A under influence of welding heat for welding the base member 26 and the circumferential joint flange 28 as well as the circumferential joint flange 28 and a plurality of reinforcing member 30, as shown FIG. 6( a) viewed from a side of the one of surfaces 26A of the base member 26. It should be noted that degree of protrusion is exaggerated for describing a step of the present invention in FIG. 6( a), as well as in FIG. 7( a) which will be described later.

In the first step of eliminating distortion, distortion in the joint structure 22 may be eliminated by applying opposing forces indicated by arrows in FIG. 6( a) to both ends and to a center part in a long side direction of the joint structure 22. Force applied to the center part in the long side direction may be one in a direction toward a flange surface 28B from the non-flange surface 28A, and force applied to both ends in the long side direction may be one in a direction toward the non-flange surface 28A from the flange surface 28B. In particular, the first step of eliminating distortion may be achieved by applying a force in a direction toward the flange surface 28B with for an example a hydraulic jack at the center part of the long side 26L of the base member 26, while holding both ends in the long side direction of the flange surface 28B of the joint structure 22 with a latching tool. The joint structure 22 without distortion in the flange surface 28B, i.e. with an accurately flat flange surface 28B as shown in FIG. 6( b) may be thus obtained. This step of eliminating distortion is done before coupling the joint structure 22 and the sidewall plate 12 because it is substantially not possible to eliminate distortion after coupling them.

Although it is shown as forces perpendicular to the non-flange surface 28A and the flange surface 28B of the circumferential joint flange 28 are applied in FIG. 6, direction of applying force is not limited as such. There may be a case where a force with an appropriate angle is applied from a direction perpendicular to the non-flange surface 28A/flange surface 28B depending on condition of distortion in the joint structure 22.

(Third Step of Eliminating Distortion)

FIG. 7 shows a third step of eliminating distortion for eliminating distortion in another direction in a fabricated joint structure 22. The joint structure 22 may be distorted as that a center part of the base member 26 in a long side (26L) direction protrudes to a side of the circumferential joint flange 28 under influence of shrinking due to welding heat as described in the above, as shown FIG. 7( a) viewed from a side of the non-flange surface 28A of the circumferential joint flange 28.

To address this, in the third step of eliminating distortion, distortion in the joint structure 22 may be eliminated by applying opposing forces indicated by arrows in FIG. 7( a) to both ends and to a center part in a long side direction of the joint structure 22. Force applied to the center part in the long side direction may be one in a direction toward another surface 26B on the opposite side of one of surfaces 26A from the one of surfaces 26A of the base member 26, and force applied to both ends in the long side direction may be one in a direction toward the one of surfaces 26A from the surface 26B of the base member 26. In particular, the third step of eliminating distortion may be achieved by applying a force in a direction toward the other surface 26B with for an example a hydraulic jack at the center part of the long side 28L of the circumferential joint flange 28, while holding both ends in the long side direction of the other surface 26B of the joint structure 22 with a latching tool. The joint structure 22 without distortion in the other surface 26B of the base member 26, i.e. with an accurately flat surface 26B as shown in FIG. 7( b) may be thus obtained.

Although it is shown as forces perpendicular to the one of surfaces 26A and the other surface 26B of the base member 26 are applied in FIG. 7, direction of applying force is not limited as such. There may be a case where a force with an appropriate angle is applied from a direction perpendicular to the one of surfaces 26A and the other surface 26B depending on condition of distortion in the joint structure 22.

When considering only prevention of leakage of fluid in a bulk fluid storage tank 1, the third step of eliminating distortion is not necessarily be performed. It is because that leakage of fluid in a bulk fluid storage tank 1 occurs when, in general, a flange surface 28B of a circumferential joint flange 28 is not accurately flat. Thus, as long as the flange surface 28B is flat, distortion in a joint structure 22 does not immediately cause leakage of fluid in the bulk fluid storage tank 1 even if the joint structure 22 is distorted as to protrude to a direction perpendicular to the one of surfaces 26A or the other surface 2613 of the base member 26. In this regard, the third step of eliminating distortion may be abbreviated.

(Step of Forming a Second Joint Structure)

Then, a second joint structure may be formed with a step in a series of the steps of forming a first joint structure, first step of eliminating distortion, and third step of eliminating distortion as necessary. Here, a joint structure 24 shown in FIG. 3 may be the second joint structure.

A sidewall plate 12 may be curved as to have a predetermined curvature depending on a number of the sidewall unit 10 used to fabricate the fluid storage tank 1. When the sidewall plate 12 is used for the fluid storage tank 1 of cylindrical member stack-type shown for example in FIG. 1, long sides thereof may be curved to be arc, and when the sidewall plate 12 is used for the fluid storage tank 1′ of single cylindrical member type shown for example in FIG. 2, short sides thereof may be curved to be arc. A method well-known to those in the art may be used for curving the sidewall plate 12.

(Step of Assembling Sidewall Units)

Next, in a step of assembling sidewall units, the sidewall plate 12, the first joint structure 22 and the second joint structure 24 may be coupled. The step of assembling sidewall units includes a step of welding to couple an edge 14 which is one of opposing circumferential edges 14, 16 of the curved sidewall plate 12 and the long side 26L of the base member 26 of the first joint structure 22 and welding to couple an edge 16 which is the other of the opposing circumferential edges 14, 16 of the curved sidewall plate 12 and the long side 26L of the base member 26 of the second joint structure 24. From a view point of durability against inner pressure acting on the fluid storage tank 1, it is preferable that the circumferential edges 14, 16 of the sidewall plate 12 and the joint structures 22, 24 are coupled so that the other surface 26B of the base member 26, i.e. the surface facing inside of the fluid storage tank 1, is approximately flush with the surface 12B of the sidewall plate 12 facing inside the fluid storage tank 1.

(Auxiliary Step of Eliminating Distortion)

In the sidewall unit according to the present invention, a length of the short side 26S of the base member 26 in the joint structure 22 shown for example in FIG. 4A is preferably one which welding heat for welding the long side 26L of the base member 26 of the joint structure 22 and the circumferential edge 14 of the sidewall plate is transferred to the circumferential joint flange 28. It is because that if welding heat is transferred to the circumferential joint flange 28, there is a risk of distortion generated in the flange surface 28B of the circumferential joint flange 28. However, there is a case where welding heat is unavoidably transferred to the circumferential joint flange 28 and distortion occurs and remains in the circumferential joint flange 28 in the sidewall unit 10 after coupling the sidewall plate 12 and the joint structure. Even in a case where distortion due to coupling the sidewall plate and the joint structure is not generated, distortion from a step before coupling may not be completely eliminated.

In one embodiment of the present invention, a fabricating method of a sidewall unit may include an auxiliary step of eliminating distortion for eliminating the above mentioned distortion. This step may be one or both of the first step of eliminating distortion and/or the third step of eliminating distortion.

(2) Second Embodiment Fabricating with Temporary Assembling

A fabricating method according to a second embodiment of the present invention may comprise a combined step of a first step of eliminating distortion and a step of forming a first joint structure, a step of forming a second joint structure and a step of assembling sidewall unit. In addition, the method may comprise a second step of eliminating distortion, a third step of eliminating distortion and/or an auxiliary step of eliminating distortion. In the fabricating method according to the second embodiment, unlike the fabricating method according to the first embodiment, an intermediate structure which a base member 26, a circumferential joint flange 28 and a plurality of reinforcing members 30 are temporarily coupled with each other is made, and each of the members is coupled (in contrast to the temporary coupling, it may be called as final coupling) after two intermediate structures are temporarily assembled and restrained. The members of the intermediate structure are welded and welded parts are cooled while two intermediate structures are restrained to restrict occurrence of distortion during cooling. As a result, a joint structure which distortion is eliminated therefrom may be fabricated.

(Combined Step of a First Step of Eliminating Distortion and a Step of Forming a First Joint Structure)

A combined step of a first step of eliminating distortion and a step of forming a first joint structure is a step of forming a first joint structure while eliminating distortion. Here, the joint structure 22 shown in FIG. 4A may be the first joint structure and intermediate structures in the step may be a first intermediate structure 22′ and a second intermediate structure 22″. FIG. 8 shows the first intermediate structure 22′ and FIG. 9 shows a state where the first intermediate structure 22′ and the second intermediate structure 22″ are temporarily assembled and restrained.

In this combined step, like in the first embodiment, each of members is arranged in a predetermined position such that a non-flange surface 28A which is opposite to a flange surface 28B of a circumferential joint flange 28 is matched with one of end surfaces of two long sides 26L of a base member 26. One of surfaces 26A of the base member 26 and the non-flange surface 28A of the circumferential joint flange 28 are arranged to intersect at a predetermined angle. In addition, a plurality of reinforcing member 30 is arranged with a predetermined interval with each other on a side of an inner angle formed by the non-flange surface 28A of the circumferential joint flange 28 and the one of surfaces 26A of the base member 26. It is preferable that the plurality of reinforcing member 30 is arranged such that a main surface a reinforcing member 30 is perpendicular to both of the one of surfaces 26A and the non-flange surface 28A. A positional relationship between a long side 28L of the circumferential joint flange 28 and a long side 26L of the base member 26 may be substantially parallel.

Then, as shown in FIG. 8, the long side 26L of the base member 26 and the non-flange surface 28A of the circumferential joint flange 28, the one of surfaces 26A and a first edge 30A of the reinforcing member 30, and the non-flange surface 28A the circumferential joint flange 28 and a second edge 30B of the reinforcing member 30 are all temporarily coupled by welding. Here, temporary coupling means the base member 26, the circumferential joint flange 28 and the plurality of reinforcing member 30 are arranged at a desired positional relationship with each other and welded at a minimum strength sufficient to maintain the positional relationship. Temporary coupling may be achieved by welding for example 2 cm of a position to be coupled. The first intermediate structure 22′ shown in FIG. 8 is formed as such.

Order of temporary coupling the base member 26, the circumferential joint flange 28 and the plurality of reinforcing member 30 is not limited. In one embodiment, the temporary coupling the base member 26, the circumferential joint flange 28 and the plurality of reinforcing member 30 may be performed in an order as that the circumferential joint flange 28 is temporarily coupled with each of the plurality of reinforcing member 30, then the circumferential joint flange 28 is temporarily coupled with the base member 26, and lastly the plurality of reinforcing member 30 is coupled with the base member 26. In another embodiment, the temporary coupling the base member 26, the circumferential joint flange 28 and the plurality of reinforcing member 30 may be performed in an order as that the base member 26 is temporarily coupled with the circumferential joint flange 28, then each of the plurality of reinforcing member 30 is coupled with the base member 26 and the circumferential joint flange 28. From a view point to minimize generation of distortion due to welding heat, it is preferable that the temporary coupling the base member 26, the circumferential joint flange 28 and the plurality of reinforcing member 30 may be sequentially performed from coupling points in vicinity of center with respect to the long side 28L of the circumferential joint flange 28 toward coupling points on the short side 28S.

Next, a second intermediate structure 22″ is formed with a similar step as forming the first intermediate structure 22′. In this embodiment, the second intermediate structure 22″ is explained as it is estimated to finally be a different joint structure from the joint structure 24. In another embodiment, an intermediate structure which is to be a joint structure 24 may be an intermediate structure 22″, and in further embodiment, an intermediate structure, which is to be a joint structure of a counterpart coupled with the joint structure 22 via a circumferential joint structure, may be an intermediate structure 22″.

As shown in FIG. 9, the formed first intermediate structure 22′ and the formed intermediate structure 22″ are temporarily assembled and restrained via the flange surface 28B of the circumferential joint flange 28. The first intermediate structure 22′ and the intermediate structure 22″ may be retained by joining with a mechanical fastener.

Then, at least in the first intermediate structure 22′, the base member 26, the circumferential joint flange 28 and each of the plurality of reinforcing member 30 are coupled with each other (i.e. final coupling). Shrinkage of materials is generated at parts coupled by welding, as previously described. In case where each of members is not temporarily assembled or retained and is coupled in a single state as a joint structure on one side, like in the first embodiment, distortion as the center part in the long side direction of the circumferential joint flange 28 protruding to a side of the non-flange surface 28A is generated, as shown in FIG. 6( a). In the first embodiment, generated distortion may be eliminated by applying force indicated by an arrow in FIG. 6( a) to a first joint structure after forming thereof. In the second embodiment, by coupling the first intermediate structure 22′ and the second intermediate structure 22″ under restraint, welding and subsequent cooling of the members are performed with force indicated by an arrow in FIG. 6( a) being constantly applied to both of the first intermediate structure 22′ and the second intermediate structure 22″. Although distortion in the circumferential joint flange 28 generally occurs when cooling, the first joint structure may be formed while eliminating distortion (or, restricting generation of distortion) as a result of that the two intermediate structures are restrained even when cooling.

As in the first embodiment, when the surface 26A of the long side 26 L of the base member 26 and the non-flange surface 28A of the circumferential joint flange 28 are welded, a force to reduce an inner angle formed by the surface 26A and the non-flange surface 28A to be smaller than a predetermined angle acts onto the base member 26 and the circumferential joint flange 28. But, in the present invention, since a plurality of reinforcing member 30 which an angle formed by a first edge 30A and a second edge 30B thereof is the predetermined angle is standing between the surface 26A and the non-flange surface 28, the angle formed therebetween may be maintained against shrinkage which occurs during cooling of welding heat.

In addition, as in the first embodiment, order of coupling (final coupling) the base member 26, the circumferential joint flange 28 and the plurality of reinforcing member 30 is not limited. In one embodiment, the coupling the base member 26, the circumferential joint flange 28 and the plurality of reinforcing member 30 may be performed in an order as that the circumferential joint flange 28 is coupled with each of the plurality of reinforcing member 30, then the circumferential joint flange 28 is coupled with the base member 26, and lastly the plurality of reinforcing member 30 is coupled with the base member 26. In another embodiment, the coupling the base member 26, the circumferential joint flange 28 and the plurality of reinforcing member 30 may be performed in an order as that the base member 26 is coupled with the circumferential joint flange 28, then each of the plurality of reinforcing member 30 is coupled with the base member 26 and the circumferential joint flange 28. From a view point to minimize generation of distortion due to welding heat, it is preferable that the coupling the base member 26, the circumferential joint flange 28 and the plurality of reinforcing member 30 may be sequentially performed from coupling points in vicinity of center with respect to the long side 28L of the circumferential joint flange 28 toward coupling points on the short side 28S.

Finally, in the temporarily assembled first intermediate structure 22′ and second intermediate structure 22″, the first intermediate structure 22′ becomes the first joint structure 22 by releasing binding by the mechanical fastener.

(Second Step of Eliminating Distortion)

In the first step of eliminating distortion and the step of forming a first joint structure, the first joint structure 22 may be formed while eliminating distortion which the center part in the long side direction of the circumferential joint flange 28 protruding to a side of the non-flange surface 28A when coupling members. But, this step may not be enough to eliminate distortion in the first joint structure. In such a case, a second step of eliminating distortion may be performed which further eliminates distortion in the first joint structure by simultaneously applying force to the center part and to both ends in the long side direction of the first joint structure 22, from the non-flange surface 28A to the flange surface 28B and from the flange surface 28B to the non-flange surface 28A, respectively. The second step of eliminating distortion may be performed with a similar procedure as the first step of eliminating distortion in the first embodiment.

In the formed first joint structure 22, there may be a case, for example, where distortion as the center part in the long side direction of the circumferential joint flange 28 is protruding to a side of the flange surface 28B depending on welding condition at temporary assembling. In such a case, the second step of eliminating distortion may be a step to further eliminate distortion in the first joint structure 22 by simultaneously applying force to the center part and to both ends in the long side direction of the first joint structure 22, from the flange surface 28B to the non-flange surface 28A and from the flange surface 28B to the non-flange surface 28A, respectively.

(Third Step of Eliminating Distortion)

In the first joint structure 22 in the second embodiment, distortion generated as the center part of the base member 26 protruding to a side of the circumferential joint flange 28 has not yet been eliminated after the first step of eliminating distortion and the step of forming the first joint structure, as shown in FIG. 7( a) viewed from a side of the non-flange surface 28A of the circumferential joint flange 28. Thus, in case where such distortion is generated, the third step of eliminating distortion may further be performed. The third step of eliminating distortion may be performed with a similar procedure as the third step of eliminating distortion in the first embodiment.

(Step of Forming a Second Joint Structure)

Next, a second joint structure may be formed with a step in a series of the first step of eliminating distortion and the step of forming the first joint structure (a second step of eliminating distortion and a third step of eliminating distortion may be performed as necessary). Here, a joint structure 24 shown in FIG. 3 may be the second joint structure.

(Other Steps)

Then, as in the first embodiment, a sidewall unit 10 is formed by bending the sidewall plate 12, coupling the sidewall plate 12 and the first joint structure 22 and the second joint structure 24, and performing auxiliary step of eliminating distortion as necessary.

3. Fabricating a Fluid Storage Tank

A fluid storage tank 1 may be fabricated using a plurality of sidewall unit 10 fabricated with a method for fabricating thereof according to the present invention and/or a plurality of sidewall unit 10 having a structure according to the present invention. The fluid storage tank 1 shown in FIG. 1 may be fabricated by stacking cylindrical members 2 formed by joining a plurality of sidewall unit 10 in circumferential direction on a separately prepared bottom wall 3 (not shown), joining the cylindrical members 2, and further stacking and mutually joining a required number of the similarly formed cylindrical members 2. A fluid storage tank 1′ shown in FIG. 2 may be fabricated by forming a cylindrical member 2′ on a separately prepared bottom wall 3′ (not shown) by joining a plurality of sidewall unit 10′ in a circumferential direction. A cat walk where a human can walk thereon and a ladder for climbing to the cat walk may be provided to the fluid storage tank 1 or 1′, although not shown. The cat walk may be used as temporary scaffolding for assembling the fluid storage tank. The following describes fabricating a fluid storage tank 1 shown in FIG. 1.

When fabricating a fluid storage tank 1 by stacking cylindrical members 2 formed by joining a plurality of sidewall unit 10 in circumferential direction, it is preferable that each of a joint structure 22 and 24 of the sidewall unit 10 is positioned to alternate in height direction in respective cylindrical member 2 as shown in FIG. 1. For example, when four sidewall units 10 are used in one cylindrical member 2 as in the fluid storage tank 1 shown in FIG. 1, it is preferable that a cylindrical member 2 at a second stage from a bottom is rotated for 45 degrees in a plane angle with respect to a cylindrical member 2 at a first stage from the bottom, and a cylindrical member 2 at a third stage from the bottom is rotated for 45 degrees in a plane angle with respect to the cylindrical member 2 at the second stage from the bottom. A cylindrical member 2 at a fourth stage may be rotated similarly with respect to the cylindrical member 2 at the third stage. As such, a well-balanced fluid storage tank 1 may be obtained by avoiding to position joining parts of the joint structures of the cylindrical members 2 in a row in height direction.

(Bottom Wall)

Structure, thickness and material of a bottom wall 3 used in a fluid storage tank are not particularly limited but may be those which allow for appropriately storing fluid inside without leakage, when used for a bulk fluid storage tank 1. In one embodiment, it is preferable that the bottom wall 3 is pre-fabricated in a plant as a plurality of unit with a predetermined size suitable for transportation, and the plurality of unit fabricated is transported to an installation site on vehicles and assembled using mechanical fasteners such as bolts and nuts. Outermost periphery of the bottom wall may be provided with a joint part for joining with a cylindrical member 2.

(Mechanical Fastener)

One cylindrical member 2 is formed by placing flange surfaces 28 of circumferential joint flanges 28 in joint structures of adjacent sidewall units 10 in opposing position and joining them using, for example, a mechanical fastener. It is preferable that adjacent joint structures are joined as providing a hole 32 in a circumferential joint flange 28 of each of the joint structures, passing a bolt in the provided hole 32 and fastening the bolt with a nut.

In general, the lower in a fluid storage tank 1, the larger inner pressure applied to a wall surface therein. Thus, it is preferable that strength for joining joint structures is larger for cylindrical members 2 in a lower part than those in an upper part of the tank. Either one or both of the following two methods may be adopted to achieve what described in the above. One of the methods is to use mechanical fastener with higher capacity for cylindrical members 2 in lower part, and the other is to use more mechanical fasteners for the cylindrical members 2 in lower part.

In case of the former, joint strength may be increased by increasing a diameter of a bolt used as a mechanical fastener. Therefore, it is preferable that a size of the hole 32 provided in the circumferential joint flange 28 of the sidewall unit 10 is larger for the flange 28 used in lower part of the fluid storage tank 1. In addition, a fastener made from a material with higher mechanical strength may be used for the cylindrical members 2 in lower part of the fluid storage tank 1.

In case of the latter, it is preferable that a number of the holes 32 provided in the circumferential joint flange 28 of the sidewall unit 10 is more for the flange 28 used in lower part of the fluid storage tank 1. In this case, it is preferable that a number of the reinforcing member 30 is more for the sidewall units in lower part of the fluid storage tank 1 fabricated by stacking the cylindrical members 2 in height direction.

(Sealing Layer)

When joining the flange surfaces 28B of the circumferential joint flange 28 in adjacent sidewall units 10 in opposing position, it is preferable to arrange a sealing layer between the opposing flange surfaces 28B for preventing leakage of fluid inside the tank. The sealing layer may preferably be, although not limited, a water-dilative elastic sealing layer, and may be arranged in areas on one or both sides of the hole 32 on the flange surface 28B corresponding to inner side or outer side of the tank. In addition, another sealing layer such as a silicon sealing layer may further be arranged in areas on one or both sides of the sealing layer corresponding to inner side or outer side of the tank.

In order to further ensure prevention of fluid leakage, for example, a groove 40 and/or 41 may be provided on the flange surface 28B of the circumferential joint flange 28 for arranging a sealing layer, as shown in FIG. 10. Arranging a sealing layer inside such provided grooves 40, 41 allows for protecting the sealing layer from being crushed even when the adjacent circumferential joint flanges 28 are strongly joined. If a sealing layer is arranged on the flange surface 28B without providing such grooves 40, 41, the sealing layer is crushed when the adjacent circumferential joint flanges 28 are strongly joined and effect of preventing fluid leakage may be deteriorated. Other advantages of providing the grooves 40, 41 are an effect to avoid drifting of the sealing layer during assembly of a fluid storage tank and an ease of aligning the adjacent circumferential joint flanges 28.

(Height-Direction Joint Flange)

In a fluid storage tank 1 fabricated by stacking a plurality of cylindrical members 2 in height direction, the cylindrical members obtained by joining a plurality of sidewall unit 10 in circumferential direction, the cylindrical members may be stacked by providing a height-direction joint flange at opposing ends in height direction of each of the sidewall unit 10 and joining the opposing flange surfaces of adjacent height-direction joint flanges with for example mechanical fasteners. When the cylindrical members 2 are stacked in height direction, flange surfaces are tightly closed with dead load of the cylindrical members 2. Since force applied to the flange surfaces by the deal load of the cylindrical members 2 is by far larger than pressure applied by fluid inside, it is enough to use a conventional ordinary joint flange for the height-direction joint flange. A height-direction joint flange for this use may be formed by welding metal plate-like structures so as to vertically stand from the sidewall unit 10 over the entire length of the end in height direction of the sidewall unit 10.

In order to increase joint strength in height direction, a steel member with a L-shaped cross section (also called an angle steel) is preferably used as a height-direction joint flange as shown in FIG. 11, mainly for the following reasons. Firstly, in a height-direction joint flange 50 using an angle steel, one of plate parts 51 is welded to a sidewall unit 10 for the entire length of two opposing long sides of the plate part 51. This separates the joining points between the height-direction joint flange 50 and the sidewall unit 10 into two (i.e. joining points between two long sides and the unit) to allow for diversifying stress and for restricting welding heat for the height-direction joint flange 50 from being transferred to the flange itself. On the contrary, a height-direction joint flange in a form of a plate welded to a sidewall unit 10 is disadvantageous in that since joining point is only one or multiple joining points are positioned close to each other, stress is prone to be concentrated and welding heat is easily transferred to a flange to cause distortion.

Secondly, a height-direction joint flange 50 using an angle steel may maintain strength even if a thickness of the plate part 52 of the flange surface is reduced, when compared with a height-direction joint flange in a form of a plate. A height-direction joint flange 50 having a flange surface with reduced thickness allows for improving air-tightness when opposing flange surfaces are joined with mechanical fasteners. On the contrary, a thickness of a flange surface of a height-direction joint flange in a form of a plate is prone to be large to hinder improving air-tightness when opposing flange surfaces are joined with mechanical fasteners.

Although not shown in FIG. 11, it is preferable that a sealing layer for preventing fluid leakage is provided in a flange surface 52 of the height-direction joint flange 50. Details such as type, arrangement and position of the sealing layer are similar to those of the circumferential joint flange 28. In addition, grooves for arranging the sealing layer may be provided as in the flange surface 28B of the circumferential joint flange 28.

DESCRIPTION OF NUMERICAL SYMBOLS

-   1, 1′: A fluid storage tank -   2, 2′: Cylindrical member -   10, 10′: Sidewall unit -   12: Sidewall plate -   14, 16: Circumferential edge -   18, 20: Edge in height direction -   22, 24: Joint structure -   22′, 22″: Intermediate structure -   26: Base member -   28: Circumferential joint flange -   30: Reinforcing member -   32: Hole -   40, 41: Groove -   50: Height-direction flange 

1. A method for fabricating a sidewall unit for use in fabricating a fluid storage tank having at least a bottom wall and a sidewall configured with one cylindrical member or by stacking a plurality of cylindrical members in height direction, at least one of the cylindrical members being configured by joining a plurality of sidewall units in circumferential direction, the method comprising: (A) a step of providing members configuring the sidewall unit, the members including: a rectangular sidewall plate; and a base member having long sides and short sides, a circumferential joint flange having long sides and short sides, and a plurality of reinforcing members having two adjacent edges which intersect at a predetermined angle included in a joint structure to be mounted to each of two opposing circumferential edges of the sidewall plate; (B) a step of forming a first joint structure by coupling the circumferential joint flange with the base member in a positional relationship where a long side of the circumferential joint flange and a long side of the base member are parallel such that a non-flange surface on the other side of a flange surface of the circumferential joint flange intersects with one of surfaces of the base member at a predetermined angle, and by coupling at least a part of each of the two adjacent edges respectively with the non-flange surface of the circumferential joint flange and the one of surfaces of the base member such that the plurality of reinforcing members stand with an interval with each other on a side of an inner angle formed by the non-flange surface of the circumferential joint flange and the one of surfaces of the base member; (C) a first step of eliminating distortion for eliminating distortion from the first joint structure by simultaneously applying a force from the non-flange surface to the flange surface and a force from the flange surface to the non-flange surface respectively to a center part and to both ends in the longitudinal direction of the first joint structure; (D) a step of forming a second joint structure by the same steps as the steps (A) to (C); and (E) a step of assembling the sidewall unit for coupling one of the opposing circumferential edges of the curved sidewall plate with the long side of the base member of the first joint structure and coupling the other of the opposing circumferential edges of the curved sidewall plate with the long side of the base member of the second joint structure.
 2. A method for fabricating a sidewall unit for use in fabricating a fluid storage tank having at least a bottom wall and a sidewall configured with one cylindrical member or by stacking a plurality of cylindrical members in height direction, at least one of the cylindrical members being configured by joining a plurality of sidewall units in circumferential direction, the method comprising: (A) a step of providing members configuring the sidewall units, the members including: a rectangular sidewall plate; and a base member having long sides and short sides, a circumferential joint flange having long sides and short sides, and a plurality of reinforcing members having two adjacent edges which intersect at a predetermined angle included in a joint structure to be mounted to each of two opposing circumferential edges of the sidewall plate; (B) a first step of eliminating distortion and forming a first joint structure to form the first joint structure while eliminating distortion, the step including; forming a first intermediate structure by temporarily coupling the circumferential joint flange with the base member in a positional relationship where a long side of the circumferential joint flange and a long side of the base member are parallel such that a non-flange surface on the other side of a flange surface of the circumferential joint flange intersects with one of surfaces of the base member at a predetermined angle, and by temporarily coupling at least a part of each of the two adjacent edges respectively with the non-flange surface of the circumferential joint flange and the one of surfaces of the base member such that the plurality of reinforcing members stand with an interval with each other on a side of an inner angle formed by the non-flange surface of the circumferential joint flange and the one of surfaces of the base member, forming a second intermediate structure by the same step as the step of forming the first intermediate structure, coupling of a circumferential joint flange, each of the plurality of reinforcing members and the base member of at least the first intermediate structure while temporary binding the first intermediate structure and the second intermediate structure, and releasing the temporary biding of the first intermediate structure and the second intermediate structure to obtain the first joint structure; (C) a step of forming a second joint structure by the same steps as the steps (A) and (B); (D) a step of assembling a sidewall unit for coupling one of the opposing circumferential edges of the curved sidewall plate with the long side of the base member of the first joint structure and coupling the other of the opposing circumferential edges of the curved sidewall plate with the long side of the base member of the second joint structure.
 3. A method according to claim 2, wherein the second joint structure is formed from the second intermediate structure.
 4. A method according to claim 2, further comprising a second step of eliminating distortion to eliminate distortion from the first joint structure, after the first step of eliminating distortion and forming a first joint structure, by simultaneously applying a force from the non-flange surface to the flange surface and a force from the flange surface to the non-flange surface respectively to a center part and to both ends in the longitudinal direction of the first joint structure.
 5. A method according to claim 1, further comprising a third step of eliminating distortion to eliminate distortion from the first joint structure by simultaneously applying a force from one of surfaces of the base member to a surface opposite to the one of the surfaces of the base member and a force from the surface opposite to the one of the surfaces of the base member to the one of the surfaces of the base member respectively to a center part and to both ends in the longitudinal direction of the first joint structure.
 6. A method according to claim 1, wherein the coupling and/or the temporary coupling of the circumferential joint flange, the base member and the plurality of reinforcing members may be performed by following a sequence of a step of coupling the circumferential joint flange with each of the plurality of reinforcing members, a step of coupling the circumferential joint flange with the base member, and a step of coupling the plurality of reinforcing members with the base member.
 7. A method according to claim 1, wherein the coupling and/or the temporary coupling of the circumferential joint flange, the base member and the plurality of reinforcing members may be performed by following a sequence of a step of coupling the circumferential joint flange with the base member, and a step of coupling each of the plurality of reinforcing members respectively with the circumferential joint flange and the base member.
 8. A method according to claim 1, wherein the coupling and/or the temporary coupling of the circumferential joint flange, the base member and the plurality of reinforcing members is sequentially performed from coupling positions in vicinity of the center part to coupling positions toward short side with respect to a long side of the circumferential joint flange.
 9. A method according to claim 1, wherein the plurality of reinforcing members are coupled such that a space between the plurality of reinforcing members is smaller in a center part than that in end parts in the long side of the circumferential joint flange.
 10. A method according to claim 1, wherein each of the plurality of reinforcing members is a panel and comprises: a first edge which is longer than a short side of a base member and is coupled with the base member and a sidewall plate; a second edge which intersects with the first edge at a predetermined angle and is coupled to the non-flange surface; a third edge which opposes to the first edge and has a length corresponding to a short side of the base member; and a fourth edge which opposes to the second edge and connects one end of the first edge with one end of the third edge.
 11. A method according to claim 10, further comprising one or both of: a step of forming a notch part in a portion corresponding to a crossing point of the first edge and the second edge; and a step of forming a notch part in a portion corresponding to a coupling point of the base member and the sidewall plate at the first edge.
 12. A method according to claim 1, wherein the base member is coupled with the circumferential joint flange so that it stands from a portion other than end parts in short side of a non-flange surface of the circumferential joint flange.
 13. A method according to claim 1, further comprising a step of forming a plurality of holes for passing mechanical fasteners over a long side of the circumferential joint flange.
 14. A method according to claim 13, wherein the plurality of holes are formed such that a diameter thereof is larger in a center part than that at an end of the long side of the circumferential joint flange.
 15. A method according to claim 1, further comprising a step of forming a groove in the flange surface of the circumferential joint flange for inserting a sealing layer.
 16. A method according to claim 1, further comprising a step of coupling a height-direction joint flange with a L-shaped cross section at opposing two ends in height direction of the sidewall unit.
 17. A sidewall unit configuring a cylindrical member, the sidewall unit used in a fluid storage tank having at least a bottom wall and a sidewall configured with one cylindrical member or by stacking a plurality of cylindrical members in height direction, the fluid storage tank being configured by joining a plurality of sidewall units in circumferential direction, the sidewall unit comprising: a curved rectangular sidewall plate; and a pair of joint structures mounted to each of two opposing circumferential edges of the sidewall plate, each of the pair of joint structures including: a base member having long sides and short sides; a circumferential joint flange having long sides and short sides; and a plurality of reinforcing members having two adjacent edges which intersect at a predetermined angle, wherein: the circumferential joint flange and the base member are coupled in a positional relationship where a long side of the circumferential joint flange and a long side of the base member are parallel such that a non-flange surface on the other side of a flange surface of the circumferential joint flange intersects with one of surfaces of the base member at a predetermined angle, each of two adjacent edges of each of a plurality of reinforcing members is coupled respectively with the non-flange surface of the circumferential joint flange and the one of surfaces of the base member such that the plurality of reinforcing members stand with an interval with each other on a side of an inner angle formed by the non-flange surface of the circumferential joint flange and the one of surfaces of the base member, and a long side of the base member in each of the pair of joint structures is coupled to each of the opposing circumferential edges of the sidewall plate.
 18. A sidewall unit according to claim 17, wherein a space between the plurality of reinforcing members is smaller in the center part than that in end parts in the long side of the circumferential joint flange.
 19. A sidewall unit according to claim 17, wherein each of the plurality of reinforcing members is a panel and comprises: a first edge which is longer than a short side of a base member and is coupled with the base member and a sidewall plate; a second edge which intersects with the first edge at a predetermined angle and is coupled to the non-flange surface; a third edge which opposes to the first edge and has a length corresponding to a short side of the base member; and a fourth edge which opposes to the second edge and connects one end of the first edge with one end of the third edge.
 20. A sidewall unit according to claim 19, wherein a notch part is formed in one or both of a portion corresponding to a crossing point of the first edge and the second edge and a portion corresponding to a coupling point of the base member and the sidewall plate at the first edge.
 21. A sidewall unit according to claim 17, wherein the base member is coupled with the circumferential joint flange so that it stands from a portion other than end parts in short side of a non-flange surface of the circumferential joint flange.
 22. A sidewall unit according to claim 17, wherein a plurality of holes for passing mechanical fasteners are formed over a long side of the circumferential joint flange.
 23. A sidewall unit according to claim 22, wherein the plurality of holes are formed such that a diameter thereof is larger in a center part than that at an end of the long side of the circumferential joint flange.
 24. A sidewall unit according to claim 17, wherein a groove is formed in the flange surface of the circumferential joint flange for inserting a sealing layer.
 25. A sidewall unit according to claim 17, wherein a height-direction joint flange with a L-shaped cross section is coupled at opposing two ends in height direction of the sidewall unit.
 26. A fluid storage tank comprising sidewall units fabricated with a method according to claim
 1. 27. A fluid storage tank comprising sidewall units according to claim
 17. 